Mechanical Separation Processes Research Articles

Recyclability of novel energy harvesting and storage technologies for IoT and wireless sensor networks

This paper aims to present a set of separation and recycling methods designed to recover valuable materials and components from innovative high-performance piezoelectric (PEG) and thermoelectric (TEG) generators and monolithic supercapacitors (SC) developed within the InComEss project. This project, a part of the European Horizon H2020 research program, focuses on creating environmentally friendly, cost-effective, and highly efficient Energy Harvesting Systems (EHSs) for powering wireless sensor networks. It combines advanced polymer-based composite materials for piezoelectric, thermoelectric, and supercapacitors, capable of harvesting and storing electrical energy from mechanical or waste heat sources. The authors initially identified key recoverable components. In PEG, these includes Polyvinylidene fluoride (PVDF), silver electrodes, polyimide, fiberglass/resin composite and copper. In TEG the highest-value components are single walled carbon nanotubes (SWCNTs) and polymeric matrices, along with the SWCNTs, while in SC, aluminium, polyethylene terephthalate (PET) and carbon particles are targeted. This paper proposes a range of separation and recycling techniques involving mechanical, thermal, and chemical processes. These methods include microwave-assisted and pyrolysis thermal processes, various mechanical fragmentation and separation processes, hydrometallurgical recovery processes, and solvent-based dissolution methods. However, a comprehensive understanding of the end-of-life waste stream of these devices is necessary for further advancements. The authors are currently conducting a thorough laboratory assessment of the recovery methods to pinpoint the most effective recyclable options. The outcomes of this assessment will be shared in a subsequent article.

Development of eco-friendly pretreatment processes for high-purity silicon recovery from end-of-life photovoltaic modules.

This study examines the efficacy of photovoltaic (PV) recycling processes and technologies for the recovery of high-purity silicon powder from waste solar modules. In order to facilitate the simplification of complex processes, such as the conventional nitric acid dissolution, solvent and ultrasonic irradiation, and solvent dissolution, a variety of mechanical separation processes have been established. These processes are designed to enhance the efficiency and effectiveness of the aforementioned processes. And a novel method for separating EVA from recycled Si powder was devised, which studied the WGS process using aqueous solutions of H2O, HNO3, and NaCl with different specific gravities. The WGS process using NaCl solution demonstrated superior performance, removing over 94% of the EVA, requiring less energy input and producing 73% less CO2 emissions compared to the thermal process. These technologies facilitate the transition towards a circular economy and bolster the implementation of carbon-neutral initiatives.

Development of Fine Particle Mechanical Separation Processes with Representative Catalyst Materials for Recycling PEM Water Electrolyzers Exploiting their Wetting Characteristics

AbstractDemand for technologies using water electrolysis to produce green hydrogen is increasing, although recycling research on membrane electrode assemblies, which contain various precious and highly critical metals, is still limited. This study therefore aims at exploiting the feasibility of fine particle separation processes based on the difference in hydrophobicity of the ultrafine materials used as catalysts in polymer electrolyte membrane electrolyzers and at providing a fundamental study with representative materials of carbon black and TiO2. Since the cathode materials including carbon black are hydrophobic and the anode materials as well as TiO2 are hydrophilic, the characterizations of their various surface properties such as zeta potentials, dispersion characteristics, and bubble coverage angle tests have been investigated. In addition, using liquid‐liquid particle extraction in a mixture model, 99 % of carbon black is recovered in the organic phase and 97 % of TiO2 is selectively separated in the aqueous phase with the help of the dispersant, sodium hexametaphosphate.

Centriselect – A novel approach for centrifugal cell separation

Abstract The separation of bio-suspensions, such as blood, is of great interest for many biomedical applications, such as the extraction of leucocytes from whole blood, the laboratory analysis of specific cells or a mixed cell suspensions from bioreactors or the preparation of cellular products for cellbased therapy. In particular, mechanical separation processes have been established for the rapid separation of biosuspensions. The principle of mechanical separation is based on the specific density of the particles or the particle size. Thus, the corresponding processes are based on centrifugation and/or filtration. The standard process to prepare blood products from whole blood donations contains several steps. First the blood is separated into different phases by centrifugation and then further separated by filters containing specific filtration layers. The shortcomings of this process is the low yield due to bio-particles remaining in the filter and the high costs for equipment due to the use of multiple devices for centrifugation and filtration. Here we present the proof of principle of an adaptive, size-selective filter that addresses the above mentioned shortcomings. The filter is designed to combine the filtration and centrifugation process within one step. Therefore a novel filtration device was designed that can be used within a standard centrifugation tube. During centrifugation, the centrifugal force changes the filtration coefficient of the filter. This can be used to separate different sized of bio-particles at different centrifugation speeds. Moreover, the cells that were hold back in the filter can be removed afterwards by increasing the centrifugation speed. In this way, the filter is created to gradually release cells of a specific size yielding in a high purity of different cell fractions.

Finite-time thermodynamics: Multistage separation processes consuming mechanical energy

We analyze limiting capabilities of mechanical separation processes using finite-time thermodynamics and obtain estimates for the lower bound of the energy consumption for systems of a given productivity. We show that this consumption does not tend to zero when the molar fraction of one of the components tends to unity. The estimates obtained are used to analyze multistage separation processes, containing recycles, especially, isotope separation systems. For such systems we obtain relations between fluxes, mass transfer surfaces, and stage number. These relations are deduced from the condition of minimum dissipation, assuming that the enrichment factor is constant. We also obtain the optimality condition for the sequence of separations needed for a multicomponent mixture in a mechanical separation systems.

Charge-separating processes by spraying water under high pressure

Spraying water under high pressure generates charge-separating processes. While cleaning tanks and vessels in which an explosive atmosphere is present, an explosion may occur in the event of a resulting discharge. Water forms electrical double layers at the phase boundaries. Mechanical separation processes dissolve the water into many drops. This leads to charge separation and the charging of the sprayed water. The mechanical separation processes include water exiting from the nozzle, hydrodynamic instability in the jet and impact with an obstacle. Given that water has many charge carriers, the charge is stronger than with solvents. Whether the charges and the resulting discharges are potentially capable of igniting an explosive atmosphere must be investigated. The aim of this research is to define the quantity and polarity of the electrostatic charges of sprayed water under high pressure. Different measurement techniques and methods are used to enable mutual validation and to generate verified measurement results of the electric field and the potential. Water of different electrical conductivity is sprayed in free space and into a grounded conductive 1 m3 vessel. Design changes to the vessel allow centric or oblique spraying. The result is intended to extend the scope of application of the German regulation TRGS 727 and the international IEC TS 60079-32-1, which refer to ignition hazards due to electrostatic charging. This project is funded by the DGUV (German Social Accident Insurance) and partners from industry.

Mechanical separation models for material recycling applications

Mechanical recycling of common materials such as plastics requires appropriate material segregation, which is usually performed adopting processes similar to those developed for mineral engineering industry. Due to the need to increment amount and quality of selection products, such processes – still developed through trial-and-error approach – are also facing improvements in order to fit with the needs of different waste flows. The work here presented deals with methodologies for virtual and practical development of mechanical separation processes and, in particular, about the preliminary definition of densimetric tables devices; for this reason, a brief review on typical waste flow is provided. The case study considered is a mixed polymeric fragmented flow comprehending two main fraction (elastomer and rigid plastics), which have been subjected to a preliminary separation test. Due to the need to optimize the process, a model for material fluidization is proposed to investigate the relevance of process parameters (e.g. air speed value) depending on material bed characteristics. After this, an image processing tool for the rapid analysis of fragments has been prepared, its scope being to find out typical shape and size characteristics, needed as input to the model, and color identification and number, which can be used for output characterization and performance analysis. Model and image processing tool together constitute the basis for process redesign, optimization and verification.

Ultrashort-pulsed laser separation of glass-silicone-glass substrates: influence of material properties and laser parameters on dicing process and cutting edge geometry

In recent years, ultrashort-pulsed lasers have increased their applicability for industrial requirements, as reliable femtosecond and picosecond laser sources with high output power are available on the market. Compared to conventional laser sources, high quality processing of a large number of material classes with different mechanical and optical properties is possible. In the field of laser cutting, these properties enable the cutting of multilayer substrates with changing material properties. In this work, the femtosecond laser cutting of phosphor sheets is demonstrated. The substrate contains a 230 µm thick silicone layer filled with phosphor, which is embedded between two glass plates. Due to the softness and thermal sensitivity of the silicone layer in combination with the hard and brittle dielectric material, the separation of such a material combination is challenging for both mechanical separation processes and cutting with conventional laser sources. In our work, we show that the femtosecond laser is suitable to cut the substrate with a high cutting edge quality. In addition to the experimental results of the laser dicing process, we present a universal model that allows predicting the final cutting edge geometry of a multilayer substrate.

Tailoring the Pressure Profile of TEA-CO2 Laser-Induced Shock Waves for Mechanical Forming and Separation Processes

For laser shock processes, the acting pressure can be increased by confining the propagation of the laser-induced plasma. Water or glass is commonly used as confinement for laser shock waves induced by Nd:YAG-lasers. This is not possible for the longer wavelength of TEA-CO2 lasers due to higher absorption coefficients. Instead, the acting pressure can be manipulated with a pressure cell above the workpiece. Two different pressure cells were designed to test the versatility of this concept. A cylindrical pressure cell design was used to confine the propagation of the laser-induced plasma and a parabolic pressure cell design was used to reflect the shock wave back to the workpiece. The effect of the pressure cells was analysed by time-resolved force measurements and evaluated for maximum force and force duration. This study shows that the cylindrical pressure cell strongly increases the maximum force while the parabolic pressure cell maximises the duration of force application. Furthermore, the pressure cells have been applied to the laser shock-based processes laser shock punching and LiSE hardness measurement. The cylindrical pressure cell strongly enhances the results of both processes, while the parabolic pressure cell shows only a minor effect.

Environmental evaluation of recycling technology and the impact of the transport of Aluminum cables

The goal of this study is to document the environmental impact of a recycling aluminum process, using the Life Cycle Assessment (LCA) methodology, in accordance with the standards of International Organization for Standardization (ISO 14040/44). Today, the life cycle impact of European generic primary and secondary aluminum are well defined through the work of the European Aluminum Association (EAA). However specific recycling processes are not available in literature. In this study, the environmental assessment of cable recycling processing is examined. The data come from a recycling plant (MTB Recycling) in France. The specific and innovative process was developed by MTB Recycling engineers and is sold as a process solution in different countries. The specificity of MTB process relies on the absence of fusion for metal refining. Nevertheless, it reaches standard aluminum purity up to 99.6%. This performance is obtained using only mechanical separation and optical sorting processes on shredder cables. Environmental impact assessment is done using ILCD Handbook recommendations. On the one hand, the study demonstrates huge environmental benefits for aluminum recycled in comparison with primary aluminum. On the other hand, the results show the harmful environmental influence of the heat refining by comparison with cold recycling process.

Mechanical and hydrometallurgical processes in HCl media for the recycling of valuable metals from Li-ion battery waste

The present work offers a study on the engineering implications of the recovery of valuable fractions from industrially collected lithium battery (LIB) waste by mechanical and hydrometallurgical processes in HCl media. Direct leaching of LIB waste provides a possibility for Li extraction, a component that is lost into the slag fraction in the state-of-art high temperature processes. The challenges arising from the heterogeneous composition of industrial battery waste are highlighted, and the behavior of main metals present such as Co, Cu, Li, Mn, Ni and Al is observed. It is shown that mechanical separation processes can form fractions rich on Cu and Al, although subsequent refining stages are necessary. Regarding direct leaching, fast kinetics were found, as complete Li dissolution can be achieved in ca. 120 min. Furthermore, high solid/liquid ratio (>1/10) is required to increase metal value concentrations, resulting in a viscous slurry due to the graphite, plastics and other undissolved materials, which challenges filtration and washing of leach residue. Neutralization of the product liquid solution (PLS) result in co-precipitation of valuable battery metals along with Fe and Al. The highest value of LIBs lies in Co, subjected for solvent extraction (SX) or direct precipitation to make an intermediate product. SX can provide selectivity whereas Na2CO3 precipitation provides a fast route for Co-Ni bulk production. Li2CO3 precipitation from the remaining PLS is possible as zabuyelite - however, due to heterogeneity of the battery waste, the recovery of Li2CO3 with battery-grade purity remains a difficult task to be achieved by direct precipitation route.

Property-based modelling and simulation of mechanical separation processes using dynamic binning and neural networks

To fully understand the possibilities and the limits of the Circular Economy (CE), a comprehensive model taking into account its different stages (product design, mechanical pre-processing, metallurgy, etc.) is required. A crucial aspect is to understand the inevitable losses at different stages of recycling. The complexity of the material streams in mechanical separation processes requires a detailed description of particles and their properties to successfully simulate unit processes. This paper presents a new approach that connects measurement-based particle properties to statistical modelling and simulation of mechanical separation processes. The proposed approach combines particle tracking with the generalization ability of neural networks. Above all, it advances the present particle binning and tracking methods utilizing property-based binning rather than liberation-based binning for modelling purposes of complex systems. In order to demonstrate the new approach, this paper uses Mineral Liberation Analysis (MLA) data from magnetic and gravity separation processes of a complex ore. The proposed approach can be integrated into present simulation platforms such as HSC Sim.

Recovery of valuable materials from spent NIMH batteries using spouted bed elutriation

In recent years, a great increase in the generation of spent batteries occurred. Then, efficient recycling ways and correct disposal of hazardous wastes are necessary. An alternative to recover the valuable materials from spent NiMH batteries is the spouted bed elutriation. The aim of this study was to apply the mechanical processing (grinding and sieving) followed by spouted bed elutriation to separate the valuable materials present in spent NiMH batteries. The results of the manual characterization showed that about 62 wt.% of the batteries are composed by positive and negative electrodes. After the mechanical separation processes (grinding, sieving and spouted bed elutriation), three different fractions were obtained: 24.21 wt.% of metals, 28.20 wt.% of polymers and 42.00 wt.% of powder (the positive and negative electrodes). It was demonstrated that the different materials present in the spent NiMH batteries can be efficiently separated using a simple and inexpensive mechanical processing.

Life Cycle Assessment of Aluminium Recycling Process: Case of Shredder Cables

Life cycle impact of European generic primary and secondary aluminium are well defined. However specific recycling processes are not available in literature. In this study, the environmental assessment of cable recycling processing is examined. The data come from a recycling plant (MTB Recycling) in France. MTB process relies only on mechanical separation and optical sorting processes on shredder cables. On the one hand, the study demonstrates huge environmental benefits for aluminium recycled in comparison with primary aluminium. On the other hand, the results show the harmful environmental influence of the heat refining by comparison with cold recycling process.

A computer‐aided methodology for the optimization of electrostatic separation processes in recycling

The rapid growth of technological products has led to an increasing volume of waste electrical and electronic equipments (WEEE), which could represent a valuable source of critical raw materials. However, current mechanical separation processes for recycling are typically poorly operated, making it impossible to modify the process parameters as a function of the materials under treatment, thus resulting in untapped separation potentials. Corona electrostatic separation (CES) is one of the most popular processes for separating fine metal and nonmetal particles derived from WEEE. In order to optimize the process operating conditions (i.e., variables) for a given multi‐material mixture under treatment, several technological and economical criteria should be jointly considered. This translates into a complex optimization problem that can be hardly solved by a purely experimental approach. As a result, practitioners tend to assign process parameters by few experiments based on a small material sample and to keep these parameters fixed during the process life‐cycle. The use of computer experiments for parameter optimization is a mostly unexplored area in this field. In this work, a computer‐aided approach is proposed to the problem of optimizing the operational parameters in CES processes. Three metamodels, developed starting from a multi‐body simulation model of the process physics, are presented and compared by means of a numerical and simulation study. Our approach proves to be an effective framework to optimize the CES process performance. Furthermore, by comparing the predicted response surfaces of the metamodels, additional insight into the process behavior over the operating region is obtained. Copyright © 2015 John Wiley & Sons, Ltd.

New characterisation method of electrical and electronic equipment wastes (WEEE)

Innovative separation and beneficiation techniques of various materials encountered in electrical and electronic equipment wastes (WEEE) is a major improvement for its recycling. Mechanical separation-oriented characterisation of WEEE was conducted in an attempt to evaluate the amenability of mechanical separation processes. Properties such as liberation degree of fractions (plastics, metals ferrous and non-ferrous), which are essential for mechanical separation, are analysed by means of a grain counting approach. Two different samples from different recycling industries were characterised in this work. The first sample is a heterogeneous material containing different types of plastics, metals (ferrous and non-ferrous), printed circuit board (PCB), rubber and wood. The second sample contains a mixture of mainly plastics. It is found for the first sample that all aluminium particles are free (100%) in all investigated size fractions. Between 92% and 95% of plastics are present as free particles; however, 67% in average of ferromagnetic particles are liberated. It can be observed that only 42% of ferromagnetic particles are free in the size fraction larger than 20mm. Particle shapes were also quantified manually particle by particle. The results show that the particle shapes as a result of shredding, turn out to be heterogeneous, thereby complicating mechanical separation processes. In addition, the separability of various materials was ascertained by a sink–float analysis and eddy current separation. The second sample was separated by automatic sensor sorting in four different products: ABS, PC–ABS, PS and rest product. The fractions were characterised by using the methodology described in this paper. The results show that the grade and liberation degree of the plastic products ABS, PC–ABS and PS are close to 100%. Sink–float separation and infrared plastic identification equipment confirms the high plastic quality. On the basis of these findings, a global separation flow sheet is proposed to improve the plastic separation of WEEE.

Recent developments in centrifuge technology

Centrifugation represents one of the main groups of mechanical particle-liquid separation processes. There are available various centrifuges for sedimentation and filtration, which are operating continuously or discontinuously. The tasks for centrifugal separation are very wide spread from liquid clarification and purification, particle thickening, solids demoistening, particle fractionating and sorting, solids washing, liquid–liquid separation to extraction of solids or liquids. Applications of centrifuges can be found in all kinds of industry, in environmental protection, water treatment, etc. In the centrifugal field mass forces are present during the separation process. This leads to specific advantages and disadvantages in comparison to competing separation processes. Research and development for centrifugal processes today has not coming to an end but several new ideas to use centrifugal forces for separation and new technical developments in this field can be observed. After description of some fundamentals and presentation of an overview of the technical variations some aspects of advantages and disadvantages of centrifuges in comparison to other separation techniques are discussed and examples for recent research and technical development as well as actual trends in the field of centrifugation are given.

Irreversible Work of Separation and Heat-Driven Separation

Estimates of the minimal necessary work of separation for mechanical separation processes and of the minimal necessary heat consumption for heat-driven separation processes with given productivity are derived in this paper. It is shown that for heat-driven processes the productivity is limited, and this limiting productivity is estimated.

Mechanical separation-oriented characterization of electronic scrap

The ever-increasing amount of electronic scrap and the steadily-decreasing contents of the precious metals used in electronics, as well as the ever-growing environmental awareness, challenges such conventional precious-metal-oriented recycling techniques as pyrometallurgy. Separation and beneficiation of various materials encountered in electronic scrap might provide a correct solution ahead. In this context, mechanical separation-oriented characterization of electronic scrap was conducted in an attempt to evaluate the amenability of mechanical separation processes. Liberation degrees of various metals from the non-metals, which are crucial for mechanical separation, were analyzed by means of a grain counting approach. It is found that the metallic particles below 2 mm achieve almost complete liberation. Particle shapes were also quantified through an image processing system. The results obtained show that the shapes of the particles, as a result of shredding, turn out to be heterogeneous, thereby complicating mechanical separation processes. In addition, separability of various materials was ascertained by a sink–float analysis. It has been shown that density-based separation techniques shall be viable in separating metals from plastics, light plastics (ABS, PS and PVC, etc.) from glass fiber reinforced resins and aluminum from heavy metals. Specifically, a high quality copper concentrate can be expected by density-based separation techniques. Moreover, FT-IR spectra of plastics pieces from the light fractions after the sink–float testing show that PC scrap primarily contains ABS, PS and PVC plastics with the density range of +1.0–1.5 g/cm3, whereas PCB scrap mainly contains glass fiber reinforced epoxy resins plastics with the density range of +1.5–2.0 g/cm3.

Homogeneous reaction of carbon disulfide ando-phenylene diamine catalyzed by tertiary amines

Synthesis of 2-mercaptobenzimidazole (MBI) was carried out by reacting o-phenylene diamine and carbon disulfide catalyzed by tertiary amine (R3N) in a homogeneous solution. Dichloromethane, chlorobenzene, chloroform, toluene, and benzene were employed as the organic solvent. The advantage of using such organic solvents is that MBI precipitates from the organic solution. Only mechanical separation processes, such as filtration and centrifugation, can be used to obtain the MBI product of high purity. Based on the reaction mechanism, a kinetic model, which included two steps of reactions in the organic phase, was proposed, i.e.: (i) a chemical equilibrium of the reaction of CS2 and R3N to produce an active intermediate (R3N(SINGLEBOND)CS2) was built up within a short period of time and (ii) this active intermediate further reacted with o-phenylene diamine to produce the desired MBI product. A combination of the zeroth order and pseudo-first-order rates law was used to describe the kinetic data. However, the reaction follows pseudo-first-order rate law at higher temperature, and the reaction follows zeroth-order rate law at lower temperature. The effects of the operating conditions on the conversion of o-phenylene diamine were also investigated. © 1996 John Wiley & Sons, Inc.